Method of silvering incandescent bulbs of the reflecting type



Nov. 25, 1952 Q FlNK 2,619,430

METHOD OF SILVERING INCANDESCENT BULBS OF THE REFLECTING TYPE Filed May 11, 1948 INVENTOR. William 6. Fin/i MK%@AM Attornqy I Patented Nov. 25, 1952 UN ITED STATES PATENT OFF 2,619,430

METHOD OF SILVER'ING INCnNDESCE-Ni' BULBS OF THE REFLECTIN G TYPE William C. Fink, Brooklyn, 'N. 1 assignor, by

mesne assignments, to sylvania Electric Broducts Inc., New York, N. Y., a corporation of Massachusetts Application May 11, 1948, 'Serial'No. 26,298

3 Claims.

This invention relates to the method and apparatus for forming silver reflecting coatings on glass surfaces by chemical deposition and more particularly to the formation of such coatings on the interior surfaceof glass bulbs such as used in the incandescent lamp fields.

The chemical deposition of silver either for decorative purposes or for purposes of producing high reflecting surfaces is a well established art. Procedures have been developed, in accordance with which, the interior surfaces of glass bulbs, such as are used as reflector type lamps in the incandescent lamp field, can be satisfactorily coated even though glass surfaces require a more perfect finish than is normally the custom in the silverin art. Heretofore, when silvering the interior surfaces of glass bulbs for the production of reflector type lamps, the entire inner surface of the bulb including the dome through which the light is to be transmitted, was silver coated. In accordance with this procedure, the silvering solution and the reducing solution were poured into the flask or bulb which was then stoppered and subjected to a vigorous shaking operation for a definite period whereupon the solutions were withdrawn leaving a silver deposit on the entire inner surface of the glass envelope.

Since the primary function of these glass bulbs is to produce light, which is to be transmitted through the dome or flatter portions of the glass envelope, it was of course necessary to provide some means for removing the silver at the point where a window was to be provided for the transmission of the light generated within the envelope.

To accomplish this it was customary, in accordance with prior art practice, to take the silvered glass bulb, which had been rinsed after the silvering operation, and place it neck side up on a table or other horizontal surface thus forming a, flask like container. When in this position, a small amount of acid capable of dissolving silver, was introduced with care into the bulb or glass envelope in sufficient amount to bring the liquid level up to t e point on the side of the envelope which was to form the margin between the silvered surface and the transparent window. Care would naturally have to be taken that no acid touched the side walls of the envelope to prevent any of the acid from 2 dissolving silver at points not desired and thus deleteriously affect the desired-reflecting surface. After the acid had been permitted to remain :in the envelope for sufficient time to dissoi-v-e the silver with which it was in contact, i'n'e'ans usually of the suction type would be carel iiny inserted into the glass bulb to withdraw the "acid and the dissolved silver, whereupon the in 'rior of the envelope would have to be carefully used to remove all traces of the acid without solving too much of the silver at the marg edges between the window and the reheating side surfaces of the bulb.

From this description it can readily be seen that this process is hardly an ideal one from a commercial viewpoint in that the technique used for removing the undesired silver is much too delicate to lend itself to high speed techniques Without at the same time lowering the standards of quality.

Somewhat similar 'di'ffi'cul'ties a'nd tricky techniques are encountered in the .prior a'rt'metl-rods of making indirect reflector type incandescent bulbs. In this case the segment of the bulb which is silvered is the dome area while the remaining part of the bulb must be free of silver. This type of bulb was made in a similar time consuming expensive way in which the entire bulb is first silvered 'wher'e'upon the silver is cut out from the undesired segment by means of an acid bath. To do this, the bulb is held dome side up while acid is forced up inte -it until it reached the desired height, left there for the necessary time to remove the silver and then withdrawn.

It is an object of this invention to improve the techniques of manufacturing silvered reflector type lamps.

It is a further object of this invention to provide a method of manufacturing such lamps which there will be no need for making use of acid etches or acid cutting baths.

In accordance with this invention, it has been found that these and other advantages can be obtained if the silvering process is carried out by a controlled flush method.

To present a better understanding of the iiivention, particular embodiments thereof will now be described in connection with the accompanying drawings in which:

Fig. 1 is a perspective view of a rotating bulb over the inner surface of which a silvering solution is being flushed;

Fig. 2 is a perspective view of a modified structure for flushing silverin solution onto an annular zone of a bulb;

Fig. 3 is a perspective view showing the method of silvering an indirect reflector type incandescent lamp.

In accordance with a preferred embodiment of this invention, as exemplified in Fig. 1 the reducing solution and the silvering solution are brought into the interior of the glass bulb to be silvered through separate stationary pipes and nozzles which cause the solutions to be flushed onto the side walls of the glass envelope. A similar result could, of course, be obtained if the envelope were held stationary and the spray nozzles, through which the silvering solution and the reducing solutions are introduced into the glass envelope, were revolved. It has been found that by operating in this manner it is readily possible to coat only that area of the glass envelope which is to be used as the reflecting surface and to leave that portion of the envelope, through which the light is to be transmitted, free of silver, thereby eliminating all need for removing silver from unwanted places by means of acid. Furthermore, by this method, it is possible to obtain a very clean out line of demarcation between the reflecting surface and the window portion of the glass bulb. In accordance with this embodiment of the invention, the glass bulb I is supported by a series of circumferentially spaced rollers H which hold it with its neck down. Rollers l3 which also engage the side walls of the bulb iii are motor driven through shaft [5 and cooperatively hold and rotate the bulb during the silvering operation.

The silvering solution and the reducing solution which are brought into the glass bulb through tubes 12 and M are then caused to commingle shortly before they are flushed up against the side of the bulb with their trajectories so positioned that the commingled solution will not reach .a point higher than point 16 on the side of the bulb thus leaving exposed the entire dome l8 of the bulb for the transmission of light.

As the bulb rotates, the solution is flushed onto the side surfaces of the bulb below the point 16. Centrifugal force developed by the rotation of the bulb tends to keep the solution on the side walls of the bulb while the force of gravity ultimately causes the solution to flow down through the neck of the bulb and empty out. Meanwhile because of the rotation of the bulb and the reducing action of the agent on the silvering solution the entire side surface of the bulb is coated with silver. Due to the nature of the solution, an opaque pin hole free, clean, bright coating is obtained which has a high quality and which can withstand the heat to which incandescent lamps must be subjected in manufacture and use.

In order to obtain good results by this method, it'is-desirable that the solutions used give an exceedingly rapid reduction action. Therefore, in preferred embodiments of the invention, the solutions are not mixed with each other before they are applied to the glass, that is to the interior of the bulb. They are, therefore, usually brought therein in separate streams which unite after they issue from their respective nozzles and immediately before they reach the surface to 45. r to permit it to spin when the solutions from nozbe silvered. This is done either in the form of an atomized spray or as an unatomized solid jet. .Llns reduces to a minimum any reduction of the silver otherwise than at the surface to be coated. In this way, a very substantial saving in the quantities of the solution used as well as an increase in the speed OI deposition is affected. It will, of course, be understood that the actual method of this invention need not be limited to one in which the solutions are brought into the interior of the bulb in two dillerent and separate tubes. l'here is no reason, other than that 01' economy, why the silverlng and reducing solutions cannot be mixed and sent into the interior or the bulbs through a single tube and thence sprayed onto the side wall or the tube.

lhe essential characteristics of this embodiment of the invention lies in the fact that either the bulb is caused to rotate about the means by which the silvermg solution is brought into contact with the side walls or the glass bulb, or the means by which the silvering solution is brought to the interior of the glass bulb is caused to rotate with respect to the glass bulb and thereby insure a uniform distribution of the silver over the entire side wall area without simultaneously depositing silver on the dome of the bulb.

In accordance with the embodiment of the invention shown in Fig. 2 of the drawings the general flush pattern is achieved by causing the two solutions to impinge upon a deflector plate which directs the commingled solutions in annular directions onto the side walls of the bulb but protects the dome of the bulb.

With this latter modification, it is also possible to coat the side reflecting wall of the bulb without later having to remove unwanted silver from the dome area of the bulb. When operating in accordance with the modification it is not necessary for either the bulb or the nozzle to revolve with respect to one another, since the flush pattern is annular. However, to insure a uniform pattern it has been found desirable to cause the deflecting plate 22 to be so mounted as zle 24 and 26 impinge upon it. Inclined vanes 23 on the deflector plate help produce the desired spin and uniformity of pattern.

The flush method of silvering segments of reflector type lamps need not be limited to the direct reflector type lamps of the type illustrated in Fig. 1 and Fig. 2 of the drawings. The speed of operation and the other advantages inherent in this method can also be used beneficially in making indirect reflector type incandescent lamps of the type in which only the dome is silvered and the remaining portions of the envelope remain transparent. Fig. 3 of the drawings illus-- .trates a preferred embodiment of this invention in accordance with which the dome segment of the envelope can be silvered without first covering surfaces which will later have to be made transparent. In accordance with this embodiment the envelope or bulb 30 being silvered is coupled with the reaction of the silvering solution causes the silver to be deposited out in the desired segment of the bulb onto which the solutions are being flushed. Upon completion of the silvering operation, the inside of the bulb can be worked out in a similar manner with the use. of a tube for the introduction of the water and another tube for its removal similar to tube 38.

It can readily be seen that the above-described process is simple, of great commercial practicability and much less time consuming than the processes heretofore used in which deposited silver had to be removed by some tricky tech niques in order to obtain the transparent parts desired.

As can readily be seen, the silvering method of this invention has many commercial advantages. First, it makes use of a relatively fast flush process which in itself reduces the silvering operations from a matter of about minutes to 60 to 90 seconds. Secondly, it completely eliminates all the other steps beyond the silverin and washing which were heretofore necessary, namely an acid etch, a wash and a drying operation which easily consumed an additional 30 to 45 minutes. Furthermore, the importance of this cannot be stressed too greatly since one of these heretofore necessary steps includes the tricky and time consuming acid treatment, which if not carried out in a very careful manner, leads to heavy shrinkage or spoilage losses.

It is of course quite apparent that the type of silvering and reducing solutions used, are not necessarily determinative of the merits of this invention, though they naturally play a large part in determining the quality of the silver deposits put onto the glass walls. The reflecting silver coating on the glass surface can be effected by the reaction at the surface of the glass of a suitable silver solution with a suitable reducing solution.

In accordance with known practice, an ammoniacal silver solution can be used which solution may comprise silver nitrate, ammonia and sodium hydroxide in the approximate proportion of 10, 5, and 3.5 and with the concentration of the silver nitrate ranging from 5 to grams per liter. It is often possible to omit the sodium hydroxide in the silver solution when sodium hydroxide is included in the reducing solution.

Various types of reducing solutions may be used and the quality of the product will vary accordingly. When good highly reflecting pin hole free opaque silver coatings are desired, it has been found desirable to make use of a solution of somewhat the following composition:

This solution contains a reducing sugar such as invert sugar or dextrose along with another suitable organic reducing compound which may be either formaldehyde or a nitroalcohol selected from the group consisting of 2-nitro Z-ethyl, l, 3 propanediol and 2-nitro-2-methal, 1-3 propanediol and 2-nitro-2 methal-l-propanol. In this solution the sugar preferably has a concentration ranging from six to 38 grams per liter and when formaldehyde is the additional reducing agent it is provided in reactive proportions to the sugar and with the sugar range as stated, its range of concentration should be from 8 to 26.5 ml. per liter. When one of the nitroalcohols is the addition reducing agent, it is provided in reactive proportions to the sugar and with the sugar range as stated its range of concentration should be from 8 to 15 grams per liter.

Example 1" a. Invert sugar or dextrose, from 6 to 38 grams per liter.

1). Formaldehyde (37 from 8 to 26.5 ml. per liter.

0. Mercuric cyanide, from 0 to 16 mg. per liter. 01. Potassium cyanide, from 0 to 10 mg. per liter.

Example 2 a. Invert sugar or dextrose, from 6 to 38 grams per liter.

1). One of listed nitro-alcohols, from 8 to 15 grams per liter:

2-nitro-2 ethyl-1, 3 propanediol 2-nitro-2-methal-1, 3 propanedlol 2-nitro-2-methal-1 propanol 1 c. Mercuric cyanide, from 0 to 16 mg. per liter. d. Potassium cyanide, from 0 to 10 mg. per liter.

e. Triethanol-amine, from 0 to 13 ml. per liter. j. Sodium hydroxide, from 0 to 1.75 grams per liter.

should not be used separately. should be used, varying in the While the above description and drawings submitted herewith disclose preferred and practical embodiments of the silvering method of this invention, it will be understood by those skilled in the art that the specific details of construction and arrangement of parts as shown and described, are by way of illustration and not to be construed as limiting the scope of the invention.

What is claimed is:

l. The method of silvering the inside surface of a selected portion of a bulb comprising rotating the bulb to be silvered on its vertical axis, ejecting separate streams of silvering and reducing solution toward each other so as to commingle, directing the commingled solutions in a predetermined direction so as to deposit the mixture on a predetermined segment of the bulb interior, rotating the bulb at a sufficient speed to keep solution on the side wall of the bulb, continuing the rotation for a sufficient period of time to effect reaction between the silvering and reducing solution whereby an opaque pinhole free bright coating is deposited on the bulb wall and simultaneously withdrawing the spent silvering solutions from within the bulb.

2. The method of silvering the inside surface of a selected portion of a bulb comprising rotating the bulb to be silvered on its vertical axis with the dome side upwards, ejecting separate streams of silvering and reducing solution toward each other so as to commingle, directing the com mingled solutions in a predetermined direction so as to deposit the mixture on a predetermined segment of the bulb interior, rotatin the bulb at a sufiicient speed to keep solution on the side wall of the bulb, continuing the rotation for a. sufficient period of time to effect reaction between the silvering and reducing solution whereby an opaque pinhole free bright coating is de posited on the bulb wall and simultaneously withdrawing the spent silvering solutions from within the bulb.

3. The method of silvering the inside surface of a. selected portion of a bulb comprising rotating the bulb to be silvered on its vertical axis with the dome side down, ejecting separate streams of silvering and reducing solution toward each other so as to commingle, directing the commingled solutions in a predetermined direction so as to deposit the mixture on a predetermined segment of the bulb interior, rotating the bulb at a sufflcient speed to keep solution on the side wall of the bulb, continuing the rotation for a sufllcient period of time to eifect reaction between the silvering and reducing solution whereby an opaque pinhole free bright coating is deposited on the bulb wall and simultaneously withdrawing the spent silvering solutions from within the bulb.

WILLIAM C. FLNK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Bart July 27, 1926 Bart Sept. 3, 1929 Biggs et al Apr. 23, 1935 Freund Dec. 8, 1936 Schneider Nov. 8, 1938 Birdseye et al Mar. 21, 1939 Deren Mar. 12, 1940 Peacock Sept. 10, 1940 Scott Feb. 25, 1941 

1. THE METHOD OF SILVERING THE INSIDE SURFACE OF A SELECTED PORTION OF A BULB COMPRISING ROTATING THE BULB TO BE SILVERED ON ITS VERTICAL AXIS, EJECTING SEPARATE STREAMS OF SILVERING AND REDUCING SOLUTION TOWARD EACH OTHER SO AS TO COMMINGLE, DIRECTING THE COMMINGLED SOLUTIONS IN A PREDETERMINED DIRECTION SO AS TO DEPOSIT THE MIXTURE ON A PREDETERMINED SEGMENT OF THE BULB 